Fin cut during replacement gate formation

ABSTRACT

A method is presented for forming a semiconductor structure. The method includes forming a plurality of vertical fins over a semiconductor layer formed over a substrate, depositing an oxide over the plurality of fins, and applying a cutting mask over a portion of the plurality of fins. The method further includes removing the oxide from the exposed portion of the plurality of fins, depositing a replacement gate stack, and etching portions of the replacement gate stack to remove exposed fins, the exposed fins forming recesses within the semiconductor layer. The method further includes depositing a spacer over the exposed fins and the recesses formed by the removed fins. A portion of the plurality of fins are cut during etching of the replacement gate stack and a portion of the oxide is removed before deposition of the replacement gate stack.

BACKGROUND

Technical Field

The present invention relates generally to semiconductor devices, andmore specifically, to FinFET devices where fins are cut duringreplacement gate formation.

Description of the Related Art

A fin metal-oxide-semiconductor field effect transistor (finMOSFET orFinFET) can provide solutions to metal-oxide-semiconductor field effecttransistor (MOSFET) scaling issues at and below, for example, the 22nanometer (nm) node of semiconductor technology. A FinFET includes atleast one narrow semiconductor fin (e.g., less than 30 nm wide) gated onat least two opposing sides of each of the at least one semiconductorfin. FinFET structures can, for example, typically be formed on either asemiconductor-on-insulator (SOI) substrate or a bulk semiconductorsubstrate.

A feature of a FinFET is a gate electrode located on at least two sidesof the channel formed along the longitudinal direction of the fin. Dueto the advantageous feature of full depletion in the fin structure, theincreased number of sides (e.g., two or three) on which the gateelectrode controls the channel of the FinFET enhances thecontrollability of the channel in a FinFET compared to a planar MOSFET.The improved control of the channel, among other things, allows smallerdevice dimensions with less short channel effects as well as largerelectrical current that can be switched at high speeds.

SUMMARY

In accordance with an embodiment, a method is provided for forming asemiconductor structure. The method includes forming a plurality ofvertical fins over a semiconductor layer formed over a substrate,depositing an oxide over the plurality of fins, applying a cutting maskover a portion of the plurality of fins, removing the oxide from theexposed portion of the plurality of fins, depositing a replacement gatestack, and etching portions of the replacement gate stack to removeexposed fins, the exposed fins forming recesses within the semiconductorlayer.

In accordance with another embodiment, a semiconductor device isprovided. The semiconductor device includes a plurality of vertical finsformed over a semiconductor layer formed over a substrate, an oxidedeposited over the plurality of fins, a cutting mask applied over aportion of the plurality of fins, where the oxide is removed from theexposed portion of the plurality of fins, and a replacement gate stack,wherein portions of the replacement gate stack are etched to removeexposed fins, the exposed fins forming recesses within the semiconductorlayer.

It should be noted that the exemplary embodiments are described withreference to different subject-matters. In particular, some embodimentsare described with reference to method type claims whereas otherembodiments have been described with reference to apparatus type claims.However, a person skilled in the art will gather from the above and thefollowing description that, unless otherwise notified, in addition toany combination of features belonging to one type of subject-matter,also any combination between features relating to differentsubject-matters, in particular, between features of the method typeclaims, and features of the apparatus type claims, is considered as tobe described within this document.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a cross-sectional view of a semiconductor structure includinga plurality of vertical fins over a substrate, each fin coated with anoxide, in accordance with an embodiment of the present invention;

FIG. 2 is a top view of the semiconductor structure of FIG. 1, inaccordance with an embodiment of the present invention;

FIG. 3 is a cross-sectional view of the semiconductor device of FIG. 1where a cutting mask is placed over the plurality of fins, in accordancewith an embodiment of the present invention;

FIG. 4 is a top view of the semiconductor device of FIG. 3, inaccordance with an embodiment of the present invention;

FIG. 5 is a cross-sectional view of the semiconductor device of FIG. 3where the oxide is selectively removed from a portion of the pluralityof fins, in accordance with an embodiment of the present invention;

FIG. 6 is a top view of the semiconductor device of FIG. 5, inaccordance with an embodiment of the present invention;

FIG. 7 is a cross-sectional view of the semiconductor device of FIG. 5where a replacement gate stack of amorphous silicon and a hard masklayer are deposited over the plurality of fins. The replacement gatestack is then patterned using a lithography and sidewall-image-transferetch process. The final replacement gate structures are formed after ananisotropic reactive ion etch (RIE) process, the cross-sectional viewalong the replacement gate taken along cut (a) shown in FIG. 9, inaccordance with an embodiment of the present invention;

FIG. 8 is a cross-sectional view of the semiconductor device of FIG. 5,after the final replacement gate etching process where exposed finswithout oxide coating are etched down to the substrate and fins coatedwith oxide are preserved, the cross-sectional view across the fins,between replacement gates taken along cut (b) shown in FIG. 9, inaccordance with an embodiment of the present invention;

FIG. 9 is a top view of the semiconductor device of FIGS. 7 and 8, inaccordance with an embodiment of the present invention;

FIG. 10 is a cross-sectional view of the semiconductor device of FIG. 7where a spacer is deposited, the cross sectional view taken along cut(a) shown in FIG. 13, in accordance with an embodiment of the presentinvention;

FIG. 11 is a cross-sectional view of the semiconductor device of FIG. 7where a spacer is deposited, the cross sectional view taken along cut(b) shown in FIG. 13, in accordance with an embodiment of the presentinvention;

FIG. 12 is a cross-sectional view of the semiconductor device of FIG. 7where a spacer is deposited, the cross sectional view taken along cut(c) shown in FIG. 13, in accordance with an embodiment of the presentinvention;

FIG. 13 is a top view of the semiconductor device of FIGS. 10-12, inaccordance with an embodiment of the present invention;

FIG. 14 is a cross-sectional view of another semiconductor device, wherea cutting mask is deposited over a portion of the plurality of fins toblock the active fin arrays, in accordance with another embodiment ofthe present invention;

FIG. 15 is a top view of the semiconductor device of FIG. 14, inaccordance with an embodiment of the present invention;

FIG. 16 is a cross-sectional view of the semiconductor device of FIG. 14where a replacement gate stack of amorphous silicon and a hard masklayer are deposited over the plurality of fins. The replacement gatestack is then patterned using a lithography and sidewall-image-transferetch process. The final replacement gate structures are formed after ananisotropic reactive ion etch (RIE) process the cross sectional viewtaken along cut (a) shown in FIG. 18, in accordance with an embodimentof the present invention;

FIG. 17 is a cross-sectional view of the semiconductor device of FIG.14, after the final replacement gate etching process where exposed finswithout oxide coating are etched down to the substrate, thecross-sectional view taken along cut (b) shown in FIG. 18, in accordancewith an embodiment of the present invention;

FIG. 18 is a top view of the semiconductor device of FIGS. 16 and 17, inaccordance with an embodiment of the present invention;

FIG. 19 is a cross-sectional view of another semiconductor device, wherea cutting mask is deposited over a portion of the plurality of fins toexpose the fin ends to be cut, in accordance with another embodiment ofthe present invention;

FIG. 20 is a top view of the semiconductor device of FIG. 19, inaccordance with an embodiment of the present invention;

FIG. 21 is a cross-sectional view of the semiconductor device of FIG. 19where a replacement gate stack of amorphous silicon and a hard masklayer are deposited over the plurality of fins. The replacement gatestack is then patterned using a lithography and sidewall-image-transferetch process. The final replacement gate structures are formed after ananisotropic reactive ion etch (RIE) process, the cross sectional viewtaken along cut (a) shown in FIG. 23, in accordance with an embodimentof the present invention;

FIG. 22 is a cross-sectional view of the semiconductor device of FIG. 14after the final replacement gate etching process where exposed finswithout oxide coating are etched down to the substrate, thecross-sectional view taken along cut (b) shown in FIG. 23, in accordancewith an embodiment of the present invention;

FIG. 23 is a top view of the semiconductor device of FIGS. 21 and 22, inaccordance with an embodiment of the present invention;

FIG. 24 is a cross-sectional view of another semiconductor device, wherea cutting mask is deposited over a portion of the plurality of fins toform a tapered device, in accordance with another embodiment of thepresent invention;

FIG. 25 is a top view of the semiconductor device of FIG. 24, inaccordance with an embodiment of the present invention;

FIG. 26 is a cross-sectional view of the semiconductor device of FIG. 24where a replacement gate stack of amorphous silicon and a hard masklayer are deposited over the plurality of fins. The replacement gatestack is then patterned using a lithography and sidewall-image-transferetch process. The final replacement gate structures are formed after ananisotropic reactive ion etch (RIE) process, the cross sectional viewtaken along cut (a) shown in FIG. 28, in accordance with an embodimentof the present invention;

FIG. 27 is a cross-sectional view of the semiconductor device of FIG.24, after the final replacement gate etching process where exposed finswithout oxide coating are etched down to the substrate, the crosssectional view taken along cut (b) shown in FIG. 28, in accordance withan embodiment of the present invention;

FIG. 28 is a top view of the semiconductor device of FIGS. 26 and 27, inaccordance with an embodiment of the present invention; and

FIG. 29 is a block/flow diagram of an exemplary method for forming afinFET structure by cutting the fins during replacement gate formation,in accordance with an embodiment of the present invention.

Throughout the drawings, same or similar reference numerals representthe same or similar elements.

DETAILED DESCRIPTION

In one or more embodiments, a method includes forming a plurality ofvertical fins over a semiconductor layer formed over a substrate,depositing an oxide over the plurality of fins, applying a cutting maskover a portion of the plurality of fins, removing the oxide from theexposed portion of the plurality of fins, depositing a replacement gatestack, and etching portions of the replacement gate stack to removeexposed fins, the exposed fins forming recesses within the semiconductorlayer.

In one or more embodiments, a semiconductor structure includes aplurality of vertical fins formed over a semiconductor layer formed overa substrate, an oxide deposited over the plurality of fins, a cuttingmask applied over a portion of the plurality of fins, where the oxide isremoved from the exposed portion of the plurality of fins, and areplacement gate stack, wherein portions of the replacement gate stackare etched to remove exposed fins, the exposed fins forming recesseswithin the semiconductor layer.

In one or more embodiments, the methods simplify the fin cut process bynot cutting the fins until the final replacement gate reactive ionetching (RIE) process. The protecting replacement dummy gate oxide isremoved in areas to be cut, so that the Si gate etch also etches theexposed fin structures. This eliminates the dense/iso loading issuesince the density of the process is defined by the gate etch process andnot just the fin cut mask. The material deposited over the fins (e.g.,replacement dummy gate oxide and gate amorphous silicon) also pins thefins so that strain relaxation is inhibited.

In one or more embodiments, the fins are cut during the gate etch. Thegates are not cut in the present invention. Instead, the gates areetched and the fins are cut. Stated differently, the present inventionutilizes a cut mask pattern assembly to allow for the cutting of finswith the replacement gate etch process.

Aspects of the present invention relate to methods of semiconductormanufacturing, and more particular aspects relate to methods of thinningand cutting fins from among arrays of fins on a substrate in order toprepare them for inclusion in FinFETs in an integrated circuit. Theprocess of forming FinFETs can be performed by producing large numbersof fins for inclusion in FinFETs. Forming large numbers of fins at oncecan simplify the manufacturing process and can result in FinFETs withmore uniform fins. While the present invention is not necessarilylimited to such applications, various aspects of the invention can beappreciated through a discussion of various examples using this context.

During semiconductor manufacturing, fin field effect transistors(FinFETs) can be formed out of a large fin array on a semiconductorsubstrate. A fin array can include many parallel fins from a layer offin material in a single step before subsequent processing divides(cuts) the fins into groups or sections. Rather than cutting target finsand target fin segments (hereinafter, target fins) by etching them away,one can cut fins by oxidizing the fin material of the target fins andconverting the target fins into nonconductive dielectric fins. Cuttingtarget fins can eliminate a conductive top part of the target fin (someof the fin, or all of the fin) so that no semiconducting part of thetarget fin can connect with the FinFET gate when the FinFET is complete.

Fins in a fin array can have one or more fin lengths and fin widths, anda variety of fin pitches, as well. Across a single semiconductor wafer,fins with various lengths, widths, and pitches can be processed (cut)simultaneously during a fin cut process, or can be cut in sequentialsteps according to embodiments of integrated circuit manufacturingflows. Groups and sections of fins left behind after cutting can beincorporated into FinFETs according to integrated circuit designs. Theprocess of cutting fins can be performed to remove long segments of somefins, or to transect shorter segments across a number of other adjacentfins, in order to achieve the desired final fin layout for theintegrated circuit. According to embodiments, fin arrays with a finpitch of 40 nm or less between fins can undergo fin cutting by oxidizingsemiconductor fins to create FinFETs. Some embodiments can have a finpitch of approximately 20 nm between fins that are cut from a fin array.Embodiments with narrow fins can have fin pitches as small as 10 nm,according to aspects of the present invention.

Creating fins in a fin array can include steps of depositing a hard maskmade of an oxide such as silicon dioxide or a nitride such as siliconnitride on a layer of fin material, creating a fin pattern in the hardmask, and etching the layer of fin material in order to expose thesubstrate beneath the fins. Fin materials can include silicon, dopedsilicon, silicon germanium alloys, and doped silicon germanium alloys,as well as other materials that can be formed into field effecttransistors.

Embodiments of the present invention can include methods that leave thehard mask on top of the semiconductor fins in the fin array after thefins are etched and before a conformal liner is deposited on top of thesemiconductor fins. Some embodiments can include methods that remove thehard mask before the conformal liner is deposited onto the semiconductorfins. The hard mask is generally a sacrificial material in the filmstack, removed before gate material is deposited onto the semiconductorfins. Embodiments of the present invention can describe processing thewafer with and without the hard mask present. Such discussions shouldnot be construed as limiting the scope of the present invention.

The semiconductor fins in the fin array can be cut in order to eliminatesome fins (or parts of some fins) to leave a pattern of active finsbehind. Active fins generally protrude above the top of a fill materialdeposited into troughs between fins in the fin array. Cutting targetfins in a fin array, such that no part of a target fin protrudes abovethe top of the fill material in the troughs, can include oxidizingtarget fins in situ rather than physically removing target fin materialby etching down to or into the substrate.

Oxidizing target fins can include oxidizing a top portion of a targetfin, or can include oxidizing all of a target fin, according toembodiments. By converting the material of target fins into anonconductive dielectric material, any semiconducting portion of atarget fin can be encapsulated by the fill material deposited betweenfins and by the dielectric material (dielectric fin) that can remain ontop of any semiconducting portion of a target fin. Further, byconverting target semiconductor fins into dielectric fins or dielectricmaterial, it is possible to reduce the height of the oxidized targetfins through a chemical etching process rather than a plasma etchingprocess if so desired. Cutting semiconductor fins by plasma etching canmodify the slope of fin sides adjacent to the target fins, influencingtheir electrical properties. In some embodiments, wet chemical etchingcan be more uniform and more selective between materials than plasmaetching, preserving fin material and fin profile during the cuttingprocess.

As used herein, “semiconductor device” refers to an intrinsicsemiconductor material that has been doped, that is, into which a dopingagent has been introduced, giving it different electrical propertiesthan the intrinsic semiconductor. Doping involves adding dopant atoms toan intrinsic semiconductor, which changes the electron and hole carrierconcentrations of the intrinsic semiconductor at thermal equilibrium.Dominant carrier concentration in an extrinsic semiconductor determinesthe conductivity type of the semiconductor.

As used herein, the term “drain” means a doped region in thesemiconductor device located at the end of the channel, in whichcarriers are flowing out of the transistor through the drain.

As used herein, the term “source” is a doped region in the semiconductordevice, in which majority carriers are flowing into the channel.

The term “direct contact” or “directly on” means that a first element,such as a first structure, and a second element, such as a secondstructure, are connected without any intermediary conducting, insulatingor semiconductor layers at the interface of the two elements.

The terms “overlying”, “atop”, “positioned on” or “positioned atop”means that a first element, such as a first structure, is present on asecond element, such as a second structure, wherein interveningelements, such as an interface structure can be present between thefirst element and the second element.

The term “electrically connected” means either directly electricallyconnected, or indirectly electrically connected, such that interveningelements are present; in an indirect electrical connection, theintervening elements can include inductors and/or transformers.

The term “crystalline material” means any material that issingle-crystalline, multi-crystalline, or polycrystalline.

The term “non-crystalline material” means any material that is notcrystalline; including any material that is amorphous, nano-crystalline,or micro-crystalline.

The term “intrinsic material” means a semiconductor material which issubstantially free of doping atoms, or in which the concentration ofdopant atoms is less than 10¹⁵ atoms/cm³.

As used herein, “p-type” refers to the addition of impurities to anintrinsic semiconductor that creates deficiencies of valence electrons.In a silicon-containing substrate, examples of n-type dopants, i.e.,impurities, include but are not limited to: boron, aluminum, gallium andindium.

As used herein, “n-type” refers to the addition of impurities thatcontributes free electrons to an intrinsic semiconductor. In a siliconcontaining substrate examples of n-type dopants, i.e., impurities,include but are not limited to antimony, arsenic and phosphorous.

As used herein, an “anisotropic etch process” denotes a material removalprocess in which the etch rate in the direction normal to the surface tobe etched is greater than in the direction parallel to the surface to beetched. The anisotropic etch can include reactive-ion etching (RIE).Other examples of anisotropic etching that can be used at this point ofthe present invention include ion beam etching, plasma etching or laserablation.

As used herein, the term “fin structure” refers to a semiconductormaterial, which can be employed as the body of a semiconductor device,in which a gate structure is positioned around the fin structure suchthat charge flows down the channel on the two sidewalls of the finstructure and optionally along the top surface of the fin structure. Thefin structures are processed to provide FinFETs. A field effecttransistor (FET) is a semiconductor device in which output current,i.e., source-drain current, is controlled by the voltage applied to thegate structure to the channel of a semiconductor device. A finFET is asemiconductor device that positions the channel region of thesemiconductor device in a fin structure.

It is to be understood that the present invention will be described interms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps/blocks may be varied within the scope of the present invention. Itshould be noted that certain features may not be shown in all figuresfor the sake of clarity. This is not intended to be interpreted as alimitation of any particular embodiment, or illustration, or scope ofthe claims.

FIG. 1 is a cross-sectional view of a semiconductor structure includinga plurality of vertical fins over a substrate, each fin coated with anoxide, in accordance with an embodiment of the present invention.

A semiconductor structure 5 includes a semiconductor substrate 10 with aplurality of fins 14, where the fins are separated by a local isolationdielectric fill layer 12. The dielectric layer 12 can be, e.g., SiO₂. Inone embodiment, a proximal portion of the fins 14 extends into the localisolation dielectric layer 12. The fins 14 extend vertically from thesubstrate 10. Stated differently, the fins 14 are normal to orperpendicular to the substrate 10. A sacrificial oxide layer 16 isdeposited on the fins 14. The oxide layer 16 encompasses or envelops thefins 14. The oxide layer contacting the top portion of the fins 14 canbe designated as 16 and the oxide layer contacting regions or troughsbetween the fins 14 can be designated as 15.

In one or more embodiments, the substrate 10 can be a semiconductor oran insulator with an active surface semiconductor layer. The substrate10 can be crystalline, semi-crystalline, microcrystalline, or amorphous.The substrate 10 can be essentially (i.e., except for contaminants) asingle element (e.g., silicon), primarily (i.e., with doping) of asingle element, for example, silicon (Si) or germanium (Ge), or thesubstrate 10 can include a compound, for example, Al₂O₃, SiO₂, GaAs,SiC, or SiGe. The substrate 10 can also have multiple material layers,for example, a semiconductor-on-insulator substrate (SeOI), asilicon-on-insulator substrate (SOI), germanium-on-insulator substrate(GeOI), or silicon-germanium-on-insulator substrate (SGOI). Thesubstrate 10 can also have other layers forming the substrate 10,including high-k oxides and/or nitrides. In one or more embodiments, thesubstrate 10 can be a silicon wafer. In an embodiment, the substrate 10is a single crystal silicon wafer.

As used herein, a “semiconductor fin” refers to a semiconductorstructure including a portion having a shape of a rectangularparallelepiped. The direction along which a semiconductor fin 14laterally extends the most is herein referred to as a “lengthwisedirection” of the semiconductor fin 14. The height of each semiconductorfin 14 can be in a range from 5 nm to 300 nm, although lesser andgreater heights can also be employed. The width of each semiconductorfin 14 can be in a range from 5 nm to 100 nm, although lesser andgreater widths can also be employed. In various embodiments, the fins 14can have a width in the range of about 6 nm to about 20 nm, or can havea width in the range of about 8 nm to about 15 nm, or in the range ofabout 10 nm to about 12 nm. In various embodiments, the fins 14 can havea height in the range of about 25 nm to about 75 nm, or in the range ofabout 40 nm to about 50 nm.

Multiple semiconductor fins 14 can be arranged such that the multiplesemiconductor fins 14 have the same lengthwise direction, and arelaterally spaced from each other along a horizontal direction that isperpendicular to the lengthwise direction. In this case, the horizontaldirection that is perpendicular to the common lengthwise direction isreferred to as a “widthwise direction.” Each semiconductor fin 14includes a pair of parallel sidewalls along the lengthwise direction anda pair of 14.

In one embodiment, each semiconductor fin 14 can be formed bylithography and etching. The lithographic step can include forming aphotoresist (not shown) atop a substrate including a topmostsemiconductor material, exposing the photoresist to a desired pattern ofradiation and then developing the exposed photoresist utilizing aconventional resist developer. The pattern within the photoresist isthen transferred into the topmost semiconductor material. The etch caninclude a dry etch process, a chemical wet etch process, or anycombination thereof. When a dry etch is used, the dry etch can be areactive ion etch process, a plasma etch process, ion beam etching orlaser ablation. The patterned photoresist material can be removed aftertransferring the pattern utilizing a conventional stripping process.

In another embodiment of the present application, each semiconductor fin14 can be formed utilizing a SIT (sidewall image transfer) process. In atypical SIT process, spacers are formed on sidewall surface of asacrificial mandrel that is formed on a topmost semiconductor materialof a substrate. The sacrificial mandrel is removed and the remainingspacers are used as a hard mask to etch the topmost semiconductormaterial of the substrate. The spacers are then removed after eachsemiconductor fin 14 has been formed. In another embodiment, sequentialSIT processes can be utilized to form fins with highly scaled fin widthand pitches.

In some embodiments, the fins in the plurality of semiconductor fins canhave a fin width between 5 nm and 10 nm. The combination of the finwidth and the width of the trough equals, in embodiments, the fin pitch.The fin width and the fin pitch can vary in different areas of a finarray, and can vary from one fin array to another on a semiconductorwafer, according to the design parameters of the integrated circuit thatis being made. For example, fins of negatively doped FinFETs can have adifferent fin size than positively doped FinFETs because of theelectrical properties of the materials they are made of.

In various embodiments, the oxide layer 16 can be silicon oxide (e.g.,SiO₂) or a silicon oxide/silicon borocarbonitride (SiBCN) bilayer, whichcan be formed by chemical vapor deposition (CVD), ALD, or a combinationthereof. The silicon oxide of the bilayer can be directly on thevertical sides of the fins 14, and the SiBCN can be formed on thesilicon oxide. In various embodiments, the portion of the oxide layer 16can be removed by chemical-mechanical polishing (CMP) and/or etching.

FIG. 2 is a top view of the semiconductor structure of FIG. 1, inaccordance with an embodiment of the present invention.

The top view illustrates the fins 14. The top view also illustrates theoxide layer 16 covering the top portion of the fins 14 and the oxidelayer 15 covering regions or troughs between the fins 14.

FIG. 3 is a cross-sectional view of the semiconductor device of FIG. 1where a cutting mask is placed over the plurality of fins, in accordancewith an embodiment of the present invention.

In various embodiments, a cutting mask 18 is placed over a portion ofthe fins 14. In one example, the cutting mask 18 is an organicplanarization layer (OPL). The OPL 18 can be formed utilizing adeposition process such as, for example, spin-on, CVD, PECVD,evaporation, chemical solution deposition and other like depositiontechniques.

The thickness of the OPL 18 can vary so long as its thickness is greaterthan the total thickness of each gate line and of the plurality of gatelines (not shown). In one embodiment, the OPL 18 has a thickness from 50nm to 500 nm. In another embodiment, the OPL 18 has a thickness from 150nm to 300 nm.

The cutting mask 18 provides robust removal of extraneous (or,undesired) features added to the first exposure's mask layout. It isunderstood that as used herein, the terms “extraneous features” and“undesired features” can be used interchangeably to describe featuresproduced in a layout (e.g., due to printing) that are not desirable inthe final layout, and also violate certain dimensional constraints(e.g., tolerances). In some cases, these extraneous features can beidentified during simulation, prior to formation of the cutting mask 18.In some cases, these extraneous features can exist at the outer contourof a process variation band (e.g., those outermost process variations).In some cases, these extraneous features can exist due to exposurevariations and/or interfering light waveforms (e.g., via constructiveinterference) that create undesired features (e.g., features) on anunderlying target. The cutting mask 18 can then be designed in order toremove these extraneous features from the final layout.

The fins not covered by the OPL 18 are designated as fins 14′. The fins14′ are the fins that will be subsequently cut during the replacementgate etching process described below. The fins 14′ can also bedesignated as target fins. The fins 14′ can reside in a region 19 notcovered by the OPL 18, as described below.

FIG. 4 is a top view of the semiconductor device of FIG. 3, inaccordance with an embodiment of the present invention.

The top view illustrates the region 19 that is not covered by the OPL18. In region 19, the fins 14′ covered by the oxide layer 16 areexposed. Additionally, some regions or troughs between the fins 14′covered by oxide layer 15 are also exposed. The region 19 represents theregion where fins 14′ will be subsequently cut during the gate etchingprocess described below.

FIG. 5 is a cross-sectional view of the semiconductor device of FIG. 3where the oxide is selectively removed from a portion of the pluralityof fins, in accordance with an embodiment of the present invention.

In various embodiments, the OPL 18 and the exposed oxide 15, 16 areetched. The etching can include a dry etching process such as, forexample, reactive ion etching, plasma etching, ion etching or laserablation. The etching can further include a wet chemical etching processin which one or more chemical etchants are used to remove portions ofthe blanket layers that are not protected by the patterned photoresist.The patterned photoresist can be removed utilizing an ashing process.

The etching results in exposing fins 14′ without any oxide thereon ortherebetween. The etching also results in exposing the oxide layers 15,16 of the fins 14 that were covered by the OPL 18.

As used herein, the term “selective” in reference to a material removalprocess denotes that the rate of material removal for a first materialis greater than the rate of removal for at least another material of thestructure to which the material removal process is being applied. Forexample, in one embodiment, a selective etch can include an etchchemistry that removes a first material selectively to a second materialby a ratio of 10:1 or greater, e.g., 100:1 or greater, or 1000:1 orgreater.

FIG. 6 is a top view of the semiconductor device of FIG. 5, inaccordance with an embodiment of the present invention.

The top view illustrates region 25 exposing the fins 14′. The top viewalso illustrates the fins 14 covered by the oxide layers 15, 16.

FIG. 7 is a cross-sectional view of the semiconductor device of FIG. 5where a replacement gate stack of amorphous silicon and a hard masklayer are deposited over the plurality of fins. The replacement gatestack is then patterned using a lithography and sidewall-image-transferetch process. The final replacement gate structures are formed after ananisotropic reactive ion etch (RIE) process, the cross-sectional viewalong the replacement gate taken along cut (a) shown in FIG. 9, inaccordance with an embodiment of the present invention.

In various embodiments, a dummy gate 20 and a hard mark 22 are depositedover the structure of FIG. 5. The dummy gate 20 can be, e.g., amorphousSi. The dummy gate 20 covers the fins 14 (having the oxide layer 16) andalso covers the fins 14′ (that are exposed; not covered by oxidelayers). A hard mask 22 is then deposited over the dummy gate 20.

The block masks can comprise soft and/or hard mask materials and can beformed using deposition, photolithography and etching. In oneembodiment, the block mask comprises a photoresist. A photoresist blockmask can be produced by applying a photoresist layer, exposing thephotoresist layer to a pattern of radiation, and then developing thepattern into the photoresist layer utilizing conventional resistdeveloper. Typically, the block masks have a thickness ranging from 100nm to 300 nm.

The block mask can comprise soft and/or hard mask materials and can beformed using deposition, photolithography and etching. In oneembodiment, the block mask is a hard mask composed of anitride-containing material, such as silicon nitride. It is noted thatit is not intended that the block mask be limited to only siliconnitride, as the composition of the hard mask can include any dielectricmaterial that can be deposited by chemical vapor deposition (CVD) andrelated methods. Other hard mask compositions for the block mask caninclude silicon oxides, silicon oxynitrides, silicon carbides, siliconcarbonitrides, etc. Spin-on dielectrics can also be utilized as a hardmask material including, but not limited to: silsesquioxanes, siloxanes,and boron phosphate silicate glass (BPSG).

In one embodiment, a block mask comprising a hard mask material can beformed by blanket depositing a layer of hard mask material, providing apatterned photoresist atop the layer of hard mask material, and thenetching the layer of hard mask material to provide a block maskprotecting at least one portion of the dummy gate 20. A patternedphotoresist can be produced by applying a blanket photoresist layer tothe surface of the dummy gate 20, exposing the photoresist layer to apattern of radiation, and then developing the pattern into thephotoresist layer utilizing resist developer. Etching of the exposedportion of the block mask can include an etch chemistry for removing theexposed portion of the hard mask material and having a high selectivityto at least the block mask. In one embodiment, the etch process can bean anisotropic etch process, such as reactive ion etch (RIE). In anotherembodiment, the replacement gate can be formed by utilizing the SITpatterning and etching process described above.

FIG. 8 is a cross-sectional view of the semiconductor device of FIG. 5,after the final replacement gate etching process where exposed finswithout oxide coating are etched down to the substrate and fins coatedwith oxide are preserved, the cross-sectional view across the fins,between replacement gates taken along cut (b) shown in FIG. 9, inaccordance with an embodiment of the present invention.

The dummy gate 20 is planarized (via, e.g., CMP) and etched back to beremoved. The dummy gate 20 has a thickness that is greater than thethickness of the fins 14. The dummy gate 20 can also have a thicknessthat is greater than the thickness of the gate hard mask 22.

The dummy gate silicon etching further results in the removal of theexposed fins 14′ (FIG. 5) and a subsequent post RIE wet clean (e.g.,dilute HF) results in the selective removal of the oxide layer 16 fromfins 14. The removal of the exposed fins 14′ results in gaps or cavitiesor recesses 23 formed between portions of the local isolation dielectricfill between fins. Therefore, the fins 14′ are cut during the etching ofthe gate structure 20. The etching can be, e.g., an RIE etch. Therefore,after the gate structure 20 is etched, an oxidation process is performedthat oxidizes the sidewall of the gate, the sidewall of the fin cut, andthe top surface of the exposed substrate. A breakthrough etch can beused to remove the top surface of the oxidized substrate and a long Sietch can be performed to increase a depth of the fin cut into thesubstrate. The protective layer around the fin can be removed by etchingor by WETs (e.g. dilute HF for SiO2). The fins 14′ can also be oxidized,instead of using the over-etching RIE process. This can turn the fin 14′within the cut region into an insulator.

RIE is a form of plasma etching in which during etching the surface tobe etched is placed on the RF powered electrode. Moreover, during RIEthe surface to be etched takes on a potential that accelerates theetching species extracted from plasma toward the surface, in which thechemical etching reaction is taking place in the direction normal to thesurface. Other examples of anisotropic etching that can be used at thispoint of the present invention include ion beam etching, plasma etchingor laser ablation.

In various embodiments, the materials and layers can be deposited byphysical vapor deposition (PVD), chemical vapor deposition (CVD), atomiclayer deposition (ALD), molecular beam epitaxy (MBE), or any of thevarious modifications thereof, for example plasma-enhanced chemicalvapor deposition (PECVD), metal-organic chemical vapor deposition(MOCVD), low pressure chemical vapor deposition (LPCVD), electron-beamphysical vapor deposition (EB-PVD), and plasma-enhanced atomic layerdeposition (PE-ALD). The depositions can be epitaxial processes, and thedeposited material can be crystalline. In various embodiments, formationof a layer can be by one or more deposition processes, where, forexample, a conformal layer can be formed by a first process (e.g., ALD,PE-ALD, etc.) and a fill can be formed by a second process (e.g., CVD,electrodeposition, PVD, etc.).

FIG. 9 is a top view of the semiconductor device of FIGS. 7 and 8, inaccordance with an embodiment of the present invention.

The top view illustrates region 25 where the gaps or cavities orrecesses 23 are exposed. The top view also illustrates the hard mask 22.

FIG. 10 is a cross-sectional view of the semiconductor device of FIG. 7where a spacer is deposited, the cross sectional view taken along cut(a) shown in FIG. 13, in accordance with an embodiment of the presentinvention.

FIG. 11 is a cross-sectional view of the semiconductor device of FIG. 7where a spacer is deposited, filling in the trenches created after thefin cut and coating the remaining standing fins between replacementgates, the cross sectional view taken along cut (b) shown in FIG. 13, inaccordance with an embodiment of the present invention.

FIG. 12 is a cross-sectional view of the semiconductor device of FIG. 7where a spacer is deposited, the cross sectional view taken along cut(c) shown in FIG. 13, in accordance with an embodiment of the presentinvention.

In various embodiments, a spacer fill takes place. A spacer etch backprocess can leave dielectric on the PC sidewall and in the fin cuttrench, but is removed from the fins, which will have EPI growth. Thespacer 24 can be, e.g., a nitride film. In an embodiment, the spacer canbe an oxide, for example, silicon oxide (SiO), a nitride, for example, asilicon nitride (SiN), or an oxynitride, for example, silicon oxynitride(SiON). In an embodiment, the spacer 24 can be, e.g., SiOCN, SiBCN, orsimilar film types. The spacer 24 can also be referred to as anon-conducting dielectric layer.

In some exemplary embodiments, the spacer 24 can include a material thatis resistant to some etching processes such as, for example, HF chemicaletching or chemical oxide removal etching. For illustrative purposes,the spacer 24 is shown as a single layer of material. Exemplaryembodiments of the spacer 24 can include, for example, multiple layersof similar or dissimilar materials that may be disposed in horizontallyor vertically arranged layers relative to the substrate 10 by anysuitable material deposition process.

In one or more embodiments, the spacer 24 can have a thickness in therange of about 3 nm to about 10 nm, or in the range of about 3 nm toabout 5 nm. Spacer thickness is selected based on a desire to pinch-offthe trench within the recessed region 23 while having a suitablethickness for device performance.

FIG. 13 is a top view of the semiconductor device of FIGS. 10-12, inaccordance with an embodiment of the present invention.

The top view illustrates the spacer 24 atop of the remaining fins 14 andthe spacer 24 within the recesses 23 (FIG. 8) of the local isolationdielectric layer 12.

FIG. 14 is a cross-sectional view of another semiconductor device, wherea cutting mask is deposited over a portion of the plurality of fins toblock the active fin arrays, in accordance with another embodiment ofthe present invention.

Another way of cutting the fin is illustrated describing patterning anarea of the fins that needs to be preserved within a macro. The term“macro” describes a designed FinFET structure. In FIG. 14, a cuttingmask or OPL 30 is deposited atop of a portion of the fins 14.

FIG. 15 is a top view of the semiconductor device of FIG. 14, inaccordance with an embodiment of the present invention.

In the top view, the OPL 30 is shown covering or masking a portion ofthe fins 14.

FIG. 16 is a cross-sectional view of the semiconductor device of FIG. 14where a replacement gate stack of amorphous silicon and a hard masklayer are deposited over the plurality of fins. The replacement gatestack is then patterned using a lithography and sidewall-image-transferetch process. The final replacement gate structures are formed after ananisotropic reactive ion etch (RIE) process the cross sectional viewtaken along cut (a) shown in FIG. 18, in accordance with an embodimentof the present invention.

In various embodiments, a dummy gate 32 and a hard mark 34 are depositedover the structure of FIG. 14. The dummy gate 32 can be, e.g., amorphousSi. The dummy gate 32 covers the fins 14 (having the oxide layer 16) andalso covers the fins 14′ (that are exposed; not covered by oxidelayers). A hard mask 34 is then deposited over the dummy gate 32.

FIG. 17 is a cross-sectional view of the semiconductor device of FIG.14, after the final replacement gate etching process where exposed finswithout oxide coating are etched down to the substrate, thecross-sectional view taken along cut (b) shown in FIG. 18, in accordancewith an embodiment of the present invention.

The dummy gate 32 is planarized (via, e.g., CMP) and etched back to beremoved. The dummy gate silicon etching further results in the removalof the exposed fins 14′ and a subsequent post RIE wet clean (e.g.,dilute HF) results in the selective removal of the oxide layer 16 fromfins 14. The removal of the exposed fins 14′ results in gaps or cavitiesor recesses 35 formed between portions of the local isolation fill 12between fins 14′. Therefore, the fins 14′ are cut during the etching ofthe gate structure 32. The etching can be, e.g., an RIE etch.

FIG. 18 is a top view of the semiconductor device of FIGS. 16 and 17, inaccordance with an embodiment of the present invention.

In the top view, the OPL 30 is shown covering or masking a portion ofthe fins 40.

FIG. 19 is a cross-sectional view of another semiconductor device, wherea cutting mask is deposited over a portion of the plurality of fins toexpose the fin ends to be cut, in accordance with another embodiment ofthe present invention.

FIGS. 19, 21, and 22 are similar to FIGS. 14, 16, and 17, respectively,and their description will be omitted for sake of clarity.

FIG. 20 is a top view of the semiconductor device of FIG. 14, inaccordance with an embodiment of the present invention.

Another way of cutting the fin is illustrated describing how the loopedends of a sidewall image transfer or quadruple patterning process wouldproceed. The fin loops 40 include a distal end 41. The OLD 30 covers ormasks a portion of the fin loops 40. The distal ends 41 remain exposedsuch that portions of the distal ends 41 can be removed to isolate eachfin 40 from adjacent fins 40.

FIG. 23 is a top view of the semiconductor device of FIGS. 21 and 22, inaccordance with an embodiment of the present invention.

The top view illustrates an exposed portion 48 of the fins 40.

FIGS. 24, 26, and 27 are similar to FIGS. 14, 16, and 17, respectively,and their description will be omitted for sake of clarity.

FIG. 25 is a top view of the semiconductor device of FIG. 24, inaccordance with an embodiment of the present invention.

In the top view, the OPL 30 is shown covering or masking a portion ofthe fins 50.

Another way of cutting the fin is illustrated describing how one canmake a macro where there are different fin lengths, some spanning 2gates and some spanning 3 gates. The fin loops 50 include a distal end51. The OLD 30 covers or masks a portion of the fin loops 50. The distalends 51 remain exposed such that portions of the distal ends 51 can beremoved to isolate each fin 50 from adjacent fins 50.

FIG. 28 is a top view of the semiconductor device of FIGS. 26 and 27, inaccordance with an embodiment of the present invention.

The top view illustrates an exposed portion 58 of the fins 50.

FIG. 29 is a block/flow diagram of an exemplary method for forming afinFET structure by cutting the fins during replacement gate formation,in accordance with an embodiment of the present invention.

At block 100, a plurality of vertical fins are formed over asemiconductor layer formed over a substrate.

At block 102, an oxide is deposited over the plurality of fins.

At block 104, a cutting mask is applied over a portion of the pluralityof fins.

At block 106, the oxide is removed from the exposed portion of theplurality of fins.

At block 108, a replacement gate stack is deposited.

At block 110, the replacement gate stack is patterned and etched to formthe replacement gates and the exposed fins are etched.

It is to be understood that the present invention will be described interms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps/blocks can be varied within the scope of the present invention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements can also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements can be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

The present embodiments can include a design for an integrated circuitchip, which can be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer can transmit the resulting designby physical mechanisms (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein can be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., SiGe. These compounds includedifferent proportions of the elements within the compound, e.g., SiGeincludes Si_(x)Ge_(1-x) where x is less than or equal to 1, etc. Inaddition, other elements can be included in the compound and stillfunction in accordance with the present embodiments. The compounds withadditional elements will be referred to herein as alloys.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present invention, as well as other variations thereof, means that aparticular feature, structure, characteristic, and so forth described inconnection with the embodiment is included in at least one embodiment ofthe present invention. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This can be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, can be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the FIGS. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the FIGS. For example, if the device in theFIGS. is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device can be otherwise oriented (rotated 90degrees or at other orientations), and the spatially relativedescriptors used herein can be interpreted accordingly. In addition, itwill also be understood that when a layer is referred to as being“between” two layers, it can be the only layer between the two layers,or one or more intervening layers can also be present.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Thus, a first element discussed belowcould be termed a second element without departing from the scope of thepresent concept.

Having described preferred embodiments of a method of device fabricationand a semiconductor device thereby fabricated (which are intended to beillustrative and not limiting), it is noted that modifications andvariations can be made by persons skilled in the art in light of theabove teachings. It is therefore to be understood that changes may bemade in the particular embodiments described which are within the scopeof the invention as outlined by the appended claims. Having thusdescribed aspects of the invention, with the details and particularityrequired by the patent laws, what is claimed and desired protected byLetters Patent is set forth in the appended claims.

What is claimed is:
 1. A method of forming a semiconductor structure,the method comprising: forming a plurality of vertical fins over asemiconductor layer formed over a substrate; depositing an oxide overthe plurality of fins; applying a cutting mask over a portion of theplurality of fins; removing the oxide from the exposed portion of theplurality of fins; depositing a replacement gate stack; and etchingportions of the replacement gate stack to remove exposed fins to formrecesses within the semiconductor layer.
 2. The method of claim 1,further comprising depositing a spacer over the exposed fins and therecesses formed by the removed fins.
 3. The method of claim 2, whereinthe spacer is a non-conducting dielectric layer.
 4. The method of claim1, wherein a portion of the plurality of fins are cut during etching ofthe replacement gate stack.
 5. The method of claim 1, wherein a portionof the oxide is removed before deposition of the replacement gate stack.6. The method of claim 1, wherein the replacement gate stack includes adummy gate and a gate hard mask.
 7. The method of claim 6, wherein thedummy gate is formed of amorphous Si.
 8. The method of claim 1, whereinthe cutting mask is an organic planarization layer (OPL).
 9. The methodof claim 1, wherein each of the plurality of vertical fins is formed bySi.
 10. The method of claim 1, wherein each of the plurality of verticalfins is formed by SiGe.